Little is known about the influence of genes on the periodontal microflora. Currently, we are studying the subgingival bacterial flora of twins pairs at age 11, 12.5, and 14 to determine both the similarity of the flora in twins when both genetic factors and environment are similar within the twin pair, and to assess changes in the flora that occur during puberty. The study of the periodontal status of adult twins presents a unique opportunity to test hypotheses regarding the bacterial etiology of periodontal diseases, and to study the influence of genes vs. environment upon the bacterial ecology of diseased and healthy periodontal sites. From the 30-50 twin pairs that will be identified each year to study genetic influences upon the expression of periodontal disease and periodontal health (Project 111), a subset of 80 pairs of monozygous (MZ) and dizygous (DZ) twins will be studied bacteriologically. Ten pairs each of MZ and DZ pairs in which both members are periodontally healthy or have mild gingivitis or localized recession will be sampled at preselected sites. The remaining twin pairs, half MZ and half DZ, in which one or both members have periodontitis (excluding suspected or verifiable JP or SP), will be sampled at diseased sites or preselected sites if healthy. Samples will be collected, dispersed, and cultured anaerobically, and randomly selected colonies will be characterized to species- or subspecies-level using polyacrylamide gel electrophoresis of cellular proteins, biochemical tests, gas chromatography, cellular fatty acid analysis, and serologic tests. The similarities in bacterial floras between MZ pair members will be compared to those between DZ pair members and statistical analysis will be done to determined whether there is in fact a genetic influence upon the ecology of the subgingival bacterial flora in periodontal health and disease. In concert with clinical characterization of the study patients and the sites sampled, it is likely that conclusions regarding the specificity of the bacterial etiology of periodontal disease may be drawn. Comparison of these data with those from the current study of pre- and post-pubertal twin pairs will provide a basis for assessing, the environmental component as well as the possible expression of genetic factors later in life.